1.4 Sea Floor Spreading

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Vocabulary

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Mid-ocean ridge: The longest chain of mountains in the world.
Sonar: A device that bounces sound waves off under water objects and then records the the echoes of these sound waves.
Sea-floor spreading: The process that continually adds new material to the ocean floor.
Deep-ocean trenches: A deep valley along the ocean floor through which oceanic crust slowly sinks towards the mantle.
Subduction: The process by which the ocean floor sinks beneath a deep-ocean trench and back into the mantle.

Outline

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Mapping the Mid-Ocean Ridge

• Use sonar to map Mid-Ocean Ridge.

Evidence of Sea-Floor Spreading

• At the mid-ocean ridge molten material rises form mantle, molten material spreads out and pushes older rock to the sides.
• Crew found rocks shaped like pillowes.
• Scientists dicovered rock that make the ocean-floor lie in patterns of magnitized, stripes.
• Scientists found out that the farther away from the ridge the older the rock is.

Subduction at Deep-Ocean Trenches

• In deep-ocean trenches subduction allowes the ocean-floor to sink back into the mantel, over tens of millions of years.

Subduction and Earth's Oceans

• The process of subdution and sea-floor spreading can change the size and shape of the ocean.
• The Pacific ocean is shrinking, because it has many trenches.
• The Atlantic ocean is getting bigger because they has few trenches.

Sonar

Evidence for sea-floor spreading